Generally, an electric vehicle receives electric power from an overhead wire through a pantograph and drives the motor to run, using the received electric power. It is known that the motor is controlled by an electric power conversion device in which an inverter, i.e., a DC-AC conversion circuit, converts the received electric power to three-phase AC power and supplies it to the motor.
Recently, because the performance of power storage elements such as a secondary battery and an electric double layer capacitor has been improved, a system is under development in which such an element is installed in the electric vehicle and the combination of the electric power in the power storage element and that from the overhead wire is used for driving the motor to run (refer, for example, to Patent Document 1). In such a system, in order to control the power flow between the overhead wire and the power storage element, used is an electric power conversion device including a DC-DC converter, i.e., a DC-DC conversion circuit.